It is anticipated that a wavelength-tunable laser that can change an oscillation wavelength will be applied in various fields, such as communications, sensing, imaging, and thus, research and development has been actively conducted in recent years. A so-called MEMS-VCSEL that controls an oscillation wavelength of a vertical cavity surface emitting laser (hereinafter referred to as VCSEL) by using micro-electromechanical systems (hereinafter referred to as MEMS) technology is a known example of such a wavelength-tunable laser. Specifically, in a MEMS-VCSEL, cavity length is changed by mechanically moving one of a pair of reflecting mirrors in such a manner as to change laser oscillation wavelength. A MEMS-VCSEL that causes an active layer to be excited by using an external light source is disclosed in NPL 1.
Such a wavelength-tunable laser has attracted attention as a light source of an optical coherence tomography (hereinafter referred to as OCT) apparatus, which is an example of a tomographic imaging apparatus. In an OCT apparatus, a wavelength (oscillation frequency) is changed (swept), and Fourier transform is performed on an interference light detection signal, so that the intensity distribution of reflected light in the depth direction of a specimen is obtained. When the wavelength is swept, light emitted from a light source needs to be coupled to a fiber that forms part of the OCT apparatus.